JPH09-317914A, published by the Japan Patent Office in 1997, discloses a seal assembly disposed between a rod guide and an outer tube of a double-tube type hydraulic shock absorber for a vehicle.
The double-tube type hydraulic shock absorber comprises a cylinder, a piston housed in the cylinder, and a piston rod connected to the piston and projecting axially from the cylinder. The outer tube is provided on the outside of the cylinder. The rod guide supports the piston rod so as to be free to slide axially while closing openings of the cylinder and the outer tube.
The seal assembly is constituted by a rubber member in which a dust lip, an oil lip, and a check seal are integrally formed.
The dust lip slides on the piston rod to prevent dust from being brought into a cylinder when the piston rod contracts with respect to the cylinder. The oil lip slides on the piston rod so as to scrape working oil off the piston rod when the piston rod elongates with respect to the cylinder. The working oil scraped off the piston rod is temporarily stored in an oil pool formed around the piston rod. The check seal is provided in a position surrounding the oil pool and discharges working oil in the oil pool to an oil reservoir provided between the outer tube and the cylinder while preventing the working oil from flowing in the opposite direction.
The check seal comprises an annular lip extending obliquely outward and seated resiliently on an annular seat surface formed on the rod guide from above. A space on the outside of the check seal is connected to the oil reservoir via a drain port which penetrates the rod guide.
The lip of the check seal lifts up from the seat surface according to a pressure in the oil pool, and causes working oil in the oil pool to flow into the oil reservoir through a gap formed between the lip and seat surface, and the drain port. When the pressure in the oil reservoir becomes higher than the pressure in the oil pool, the check seal prevents working oil in the oil reservoir from invading the oil pool by keeping the lip in contact with the seat surface using a pressure in the oil reservoir.
The prior art proposes forming tongue and groove sections in the form of plural coaxial circles in the contact faces between the lip and seat surface such that engagement of the tongue and groove sections increases a contact area between the lip and seat surface, thereby increases a sealing performance against the invasion of working oil into the oil pool from the oil reservoir.